1. Field of the Invention
This invention relates to a syringe apparatus. More particularly, the present invention is directed to a novel syringe plunger for a syringe particularly adapted for preloading with, and storage of, a fluid ready to be dispensed.
2. The Prior Art
Many aspects of modern society have come to rely upon ready-to-use products which are used once and then disposed. In many situations, the use of ready-to-use disposable items achieves considerable cost savings since time and expense is not required to clean and ready the item for reuse.
For example, in the medical and dental professions, the widespread acceptance of ready-to-use disposable items not only results in considerable cost savings, but also increases patient safety by reducing the risk of infection because of inadequate cleaning and sterilization. Moreover, having a supply of ready-to-use disposable items insures that the particular item will be immediately available when needed without waiting for the item to be prepared.
One common example of a ready-to-use disposable item widely accepted in the medical and dental professions is the preloaded disposable syringe. A wide variety of fluids, ranging from drugs stored and ready for hypodermic injection to topical agents used in the dental profession, as well as other fluids, are stored in preloaded syringes which are kept on hand waiting to be used.
As is widely understood by health-care professionals and others, many fluids, whether used in a health care or industrial setting, have a limited shelf life. Once the shelf life of a fluid stored in a preloaded syringe is reached, it is ill advised, or even unsafe, to use the preloaded syringe. Thus, health-care providers must keep only enough supply on hand as will be used prior to reaching the maximum shelf life or incur the expense of discarding unused items.
Unfortunately, in the case of preloaded syringes, there are many instances wherein the syringe itself in which the fluid is stored contributes to a shorter than usual shelf life. In many instances, the shelf life of the fluid may be extended by merely fabricating the syringe from an opaque material thus blocking out energy and the like and near light portions of the spectrum which accelerate deterioration of the fluid and its reaction with the syringe materials. In other cases, storage of fluid in a disposable syringe affects the shelf life of the fluid little, if at all.
Nevertheless, syringes which have commonly been used in the art for such applications contributed to the shortened shelf life of the fluid contained therein. For example, in the dental profession, chemicals such as phosphoric acid and hydrofluoric acid are used to etch dental materials with excellent results. Nevertheless, compositions such as these are harsh chemicals which must be properly handled and used with care. As with other compositions used in the health-care profession, these harsh chemicals are also desirably packaged in preloaded disposable syringes which are kept on hand ready for use.
The prior art type syringes used in such applications generally comprise a syringe body or barrel having a bore formed therein. A plunger is inserted into the bore and thus any fluid contained within the syringe barrel may be expelled by pushing the syringe plunger into the barrel. Since a fluid tight seal is required between the plunger and the wall of the barrel, a resilient rubber-like tip is positioned on the end of the plunger. Unfortunately, materials from which such resilient rubber-like tips are fabricated many times tend to deteriorate in the presence of solutions of phosphoric and hydrofluoric acids, or some of the alcohol or harsh solvents and resins that are used in the dental profession. Deterioration of the plunger tip leads to both contamination of the solution within the syringe as well as decreasing the efficiency of the seal between the plunger and the bore wall.
Other prior art type syringes have replaced the rubber-like tip with a generally flat, circular disk that can be made as part of the plunger so that the disc is more resistant to corrosion. This type of syringe does not, however, glide smoothly in the syringe barrel nor does it provide a seal that is as effective as the rubber-like tip syringe plungers.
Thus, the prior art has not provided a suitable syringe apparatus which combines the advantages of a smooth glide when the syringe plunger moves through the syringe barrel, as obtained with rubber-tipped plungers, with the corrosion-resistant characteristics of non-rubber tipped plungers, which are advantageous for prolonging shelf life of chemicals of a harsher nature that may be packaged and stored in such syringes.